High pressure electric discharge lamp having a fill including uranium halide



Jan; 23, 1968 v BAUER ET AL HIGH PRESSURE ELECTRIC DISCHARGE LAMP HAVING FILL INCLUDING URANIUM HALIDE Filed Feb. 26, 1965 Arnold Bauer Guido Buchwieser VE TORS BY ATTORNEY Unie dtts fine 3,365,602 HIGH PRESSURE ELETRI DiSCl-IARGE LAM? HAVENG A FELL TWCLUDENG URANIUM HAHDE Arnold Bauer and Guido Buchwieser, Augsburg, Germany, assignors to Patent-Trenhand-Gesellschaft fur Elehtrische Glzshlampen 2113311., Munich, Germany Filed Feb. 26, 1955, Ser. No. 436,424) Claims priority, application Germany, Mar. 3, H64, 1 33,736 8 Claims. (Cl. 313-229) ABSTRACT (BF THE DESCLGSURE A high-pressure light-producing lamp with solid hot electrodes and with a gaseous filling containing a uranium halide, excited in the high-pressure discharge for producing simulation of natural or white light.

At present, of all high-pressure lamps, the ones most used are high-pressure mercury vapor lamps. The envelopes of these lamps are made usually of quartz glass, and the lamps contain, beside a starting gas, a small quantity of mercury which vaporizes completely in operation of the lamp. The are is maintained at a vapor pressure of 1 to 25 atmospheres and emits, beside a proportionately weak continuum, more particularly a line spectrum with a few but very strong lines, so that the light color of these lamps differs very much from natural light and also from light which is emitted from an incandescent solid body; and color rendition is quite unsatisfactory.

For the purpose of improving color rendition and light output, it is well known to add iodides of certain metals of the first three groups of the periodic table of the elements, to the basic gas, such as mercury or a rare gas. An addition of, for instance, Nal, TH and Inl has proven good. The resonance lines of these metals complete the mercury radiation in the blue, green and yellow range of the spectrum, but there remains an undesirable deficiency in the red. Also an addition of Lil does not give any satisfactory color rendition. Besides, with increase of the number of additional components, the danger of decomposition is encountered, a result of which is that color shifting may occur during lamp life.

A sole addition of scandium iodide to the mercury filling produces white light, but for that result, however, scandium radiation must predominate. Since the vapor pressure of such an addition is proportionately unfavorable, either the thermal wall load of the burner must be high or the basic gas pressure must be low. The first measure weakens life and the latter one weakens light output.

It is an object of the present invention to provide a high-pressure discharge lamp with a luminescent addition which, in order to prevent any decomposition phenomena, consists of the fewest possible components, and use of a component which does not require'any excessive thermal load on the bulb wall and which gives high light output and good color rendition.

According to the present invention, an electric highpressure gaseous or vapor discharge lamp with solid, discharge-heated electrodes, with an envelope consisting of high-melting light-transmissive material, and with a filling containing a metal halide compound as the component to be excited, is characterized in that the component of the filling to be excited is chosen as uranium halide.

The prior art discloses as known a lamp in which metals of the 6th, 7th and 8th groups of the periodic table in the form of their halides are used as the sole lamp filling. A re-test made of the specifications has, however, shown that generally the iodides, bromides and chlorides of the respective metals mentioned in this connection, for example, molybdenum and tungsten, decompose at or before those temperatures are reached at which the electrodes will operate. In quartz iodine lamps the van Arckel cycle process gets started, utilization of which causes the metal atoms to wander from the discharge space to the electrodes, where they deposit. Also an addition of fluorides does not solve the problem because fluorine attacks the electrodes. Such a result of the re-test was to be expected since the more right an element is in the periodic table the less its aflinity to the halogens and the lower sinks the critical temperature from which a halide decomposes. Thus, there is Well known, the equilibrium reaction of tungsten halides W-I-HXSWX (X means a halogen) equals the equilibrium cons-taut K of the law of mass action in its dependency from temperature. The amount of K l is obtained for W1 for instance at 650 C. or before. Above this temperature reaction takes place mainly from right to left. Whereas a filling of tungsten iodide in an elec-trodeless discharge lamp may be excited easily, for instance through high frequency, as long as the wall temperature of the discharge envelope remains below 650 C., such a filling does not solve the problem if hot electrodes are used. Metallic tungsten deposits in the hot zones of the electrodes until the iodide is nearly decomposed according to the law of mass action. If the electrodes consist of tungsten, molybdenum or of a metal of similar afiinity to iodine, the cooler zones of the electrodes will also be sputtered and the electrode material will be deposited in the warmer zones. Now, it has been supposed that uranium standing under tungsten in the same group of the Periodic Table would be subject to the same cyclic process because of its similar chemical characteristics and that it would be suitable in discharge lamps with solid incandescent electrodes. It was much to our surprise that the chemical behavior of uranium standing below the metals much to the right in the periodic table makes an exception and is quite suitable as the filling of discharge lamps with solid hot electrodes.

Furthermore, it has been found that the emission spectrum of uranium forms, in consequence of several circumstances acting together, a quasi-continuum, which shows special advantages in respect to color quality and light output. Contrary to lamp additions used heretofore, the special intensity of uranium radiation increases in the visible range with increasing wave length, so that just as in incandescent lamps, a warm-White tone is produced. Otherwise than in incandescent lamps, however, on the infra-red range above 850 m the intensity decreases again so that for this reason a good visual efiect is obtained. The ionizing energy of'uranium is very low with 4 ev. and only that of caesium decreases below thi value. Also this latter fact serves for the visual efiect because line radiation of the atom cannot fall below the wave length of 310 mu which corresponds to that energy. Also corresponding small exciting energies below 4 ev. are advantageous for a lamp filling of the present kind because all of these levels are excited relatively stronger than, for instance, the lowest level of the basic gas of mercury of 4.7 ev. The uranium levels are excited absolutely stronger than, for instance, the levels of mercury of 7.7 ev. which are important for the visible lines if the ratio of the partial pressures of uranium to mercury, p /p is higher than about 3 X 10 As another consequence of the low ionizing voltage, the plasma attains with a uranium partial pressure, the required conductivity with considerably lower temperature. Whereas a high-pressure mercury discharge of mean load attains an axis temperature of about 6000 K., a discharge of equal vapor pressure would, in uranium only, under similar conditions do it with 2300 K. The obtainable uranium partial pressure will, however, generally be much lower so that the plasma temperature in the lamp with uranium halide will lie about 2300 K., but always considerably below 6000 K. Heat losses are, with a permanently thick rim zone of the arc, proportional to the difference between the plasma temperature and the ambient temperature. For this latter reason, heat losses in lamps with uranium addition may be reduced if compared with mercury vapor lamps.

The exceptional position of uranium is consequently due to the surprising chemical reaction of its halides and to the unexpected cooperation of diiterent circumstances which result in a combination of high light output with very good color tone and for iodide lamps with a very long life.

Beside uranium halide which does not vaporize completely, the lamp according to the present invention has also an addition of mercury vaporizing completely in operation and producing a partial pressure of several atmospheres, as well as an addition of rare gas for :facilitating starting. Another embodiment of the lamp has, beside uranium halide, a basic fi ling of xenon amounting to several atmospheres.

Reference will now be made to the accompanying drawings, wherein FIGURE 1 is a longitudinal sectional view of a highpressure discharge lamp wherein addition of uranium iodide is employed; and

FIGURE 2 is a graph showing the spectral radiant intensity of a high-pressure mercury vapor lamp with uranium bromide addition in relative unities dependent on the wave length and wall load W in w./cm.

The discharge envelope 1 consists of quartz glass and has an enclosed volume of 4.5 cm. The internal diameter of the tubular envelope, closed semi-spherically at top and bottom ends, amounts to. 17 mm. The pin electrodes 2 and 3 consist'of refractory metal, preferablyof tungsten wire of 1.5 mm. diameter, and have a conventional foil seal 4 and 5 respectively. Activation of the electrodes beyond the usual thorium addition of up to 5% should be prevented. The rare gas filling for start- .ing facilitation amounts to 20 mm. Hg of argon. The

mercury filling of 30 mg. vaporizing completely in operation produces 'a vapor pressure of about three to tour atmospheres.

The electrical and lighting data of the lamp are:

Wattage watts 400 Current intensity amps 3 Voltage volts 135 Electrode distance cm 2.0 Wall load w./cm Luminous flux l.m 36000 Efiiciency l.m./w.. 90

Whereas the mercury quantity vaporizes completely the quantity of uranium iodide addition of mg. is chosen so high that it does not vaporize completely. The height of the partial pressure of the uranium iodide depends on the wall temperature, and, consequently, on the wall load. Since uranium halide is very hygroscopic it is recommended that metallic uranium and elementary iodine or tone of the incandescent light. Because of good color rendition with very long life, the range between 7 and 12 w./cm. is preferred. Thus, the spectral energy distribution may be adjusted even with one addition only to the highpressure mercury lamp to any desired color tone in wide limits. The required wall loads are quite compatible for quartz glass or for special glasses, as Vycor and that.

even with highest expectations in respect to lamp life.

Furthermore, there may be added to a uranium halide one or several halides, as T11, 1111 NaI or ScI in order to obtain a further increase in light output and/or some change in spectral energy distribution of the lamp.

A lamp filling according to the present invention may also be used in short are lamps. The advantage of such lamps lies in a combination of higher operating voltage as in extra high-pressure mercury lamps with good color rendition as hitherto found in xenon short are lamps only. Besides, lamp output is not only much higher than in a xenon lamp, but also higher than in an extra-highpressure mercury lamp without requiring a correspond.

' ingly high operating pressure.

across 9 to 12 w./cm. radiation of the mercury lines at a 405, 436, 546 and 577/78 Inn is urged into the. background. Whereas the total radiation at 6.5 w./cm. has a slight blue effect, it takes up at 9 w./cm. the white color of daylight to change over at higher load into the warm We claim: 1. An electric high-pressure gaseous or vapor lightproducing discharge lamp with solid discharge-heated incandescent electrodes consisting of tungsten with an addition at most of 5% thorium, said lamp having an envelope or" high-melting light-transmitting material with a filling productive of white light when excited, said filling containing a metal halide compound as the component to be excited, characterized in that said component of the filling to be excited and thereby produce white light is a uranium halide.

2; An electric high-pressure gaseous or vapor lightproducing discharge lamp with solid discharge-heated inhalide in excess of quantity that vaporizes completely in' operation, and said filling containing a rare gas for facilitating starting. 7

v 3. An electric high-pressure gaseous or vapor lightproducing discharge lamp in accordance with claim 2, characterized in that the ratio of the partial pressure of uranium to mercury in operation is higher than about 3 1O 4. An electric high-pressure gaseous or vapor lightproducing discharge lamp with solid'discharge-heated incandescent electrodes, said lamp having an envelope of high-melting light-transmitting material, and with a filling productive of white light when excited, said filling consisting of a basic filling of xenon of several atmospheres, and said filling containing a metal halide compound as the component to be excited, characterized in that said component of the filling to be excited and thereby produce white light is a uranium halide.

5. An electric high-pressure gaseous or vapor lightproducing discharge lamp in accordance with claim 1, wherein said filling is essentially said uranium halide.

6. Anelectric high-pressure gaseous or vapor lightproducing discharge lamp in accordance with claim 1, characterized in that said uranium halide is specifically uranium iodide filled into the lamp. a

7. An electric high-pressure gaseous or vapor lightproducing discharge lamp in' accordance with cla'un 1, characterized in that wattage input and envelope dimensions are related to each other so that the axis temperature of the plasma lies below 6000 K.

8. An electric high-pressure gaseous or vapor lightproducing discharge lamp in accordance with claim 1, characterized in that wattage input and envelope dimen- 5 6 sions are related to each other in such manner that the FOREIGN PATENTS wall load in operation lies between 77 and 12 w./cm. 915,247 7/1946 France.

R f C1 d 464,410 7/1951 Italy.

e 1 e s. D. SCHLOSSER, Primary Examiner. UNITED STATES PATENTS 5 JAMES W. LAWRENCE, Examiner. 2,422,659 6/1947 Depew 313-54 3,234,421 2/1966 Reiling. 

